JPH08236155A - Lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide a lithium secondary battery having excellent charge and discharge cycle characteristics and preservation characteristics by adding an amine compound selected out of amine and diamine expressed by specific formulae into nonaqueous electrolyte CONSTITUTION: In a lithium secondary battery provided with a positive electrode, a negative electrode in which carbon material is used as lithium ion storage material, and nonaqueous electrolyte, at least one kind of an amine compound selected out of amine expressed by a formula I and diamine expressed by a formula II is added into the nonaqueous electrolyte. Thereby, a lithium secondary battery having excellent charge and discharge cycle characteristics and preservation characteristics is obtained, as the decomposition of the nonaqueous electrolyte hardly occurs on the surface of the negative electrode when changing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery provided with a positive electrode, a negative electrode containing a carbon material as a lithium ion storage material, and a non-aqueous electrolyte, and more particularly to a lithium secondary battery of this type. The present invention relates to improvement of a non-aqueous electrolytic solution for the purpose of improving charge / discharge cycle characteristics and storage characteristics.

[0002]

2. Description of the Related Art In recent years,
Lithium secondary batteries have been attracting attention as next-generation secondary batteries because they have advantages such as high energy density and high voltage because there is no need to consider the decomposition voltage of water. There is. As a positive electrode material (positive electrode active material) of a high voltage type lithium secondary battery, lithium-
As the transition metal composite oxide, and as the negative electrode material (lithium ion storage material), carbon materials such as graphite and coke, which are capable of electrochemically storing and releasing lithium ions, have been mainly studied.

However, the lithium secondary battery using the carbon material as the negative electrode material has a problem that the charge / discharge cycle characteristics and the storage characteristics are not good because the non-aqueous electrolyte is decomposed on the surface of the negative electrode during charging. .

The present invention has been made to solve this problem, and its purpose is to improve charge / discharge cycle characteristics and storage characteristics by adding a specific additive to a non-aqueous electrolyte. An object is to provide an excellent lithium secondary battery.

[0005]

The lithium secondary battery (the battery of the present invention) according to the present invention for achieving the above object comprises:
In a lithium secondary battery comprising a positive electrode, a negative electrode using a carbon material as a lithium ion storage material, and a non-aqueous electrolyte,
At least one amine compound selected from an amine represented by the following chemical formula 3 and a diamine represented by the following chemical formula 4 is added to the non-aqueous electrolyte.

[0006]

Embedded image

[In the formula, R ^{1 to} R ³ are the same or different from each other and represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or a phenyl group. ]

[0008]

[Chemical 4]

[Wherein, X is an alkylene group having 1 to 4 carbon atoms or a phenylene group, and R ^{4 to} R ⁷ are the same or different from each other and are a hydrogen atom, a methyl group or a phenyl group. ]

Specific examples of the amine compound represented by Chemical formula 3 or Chemical formula 4 are propylamine, butylamine, diethylamine, dipropylamine, dibutylamine, triethylamine, tributylamine, phenylamine, diphenylamine, triphenylamine, methylenediamine. , Ethylenediamine, tetramethylenediamine, o-
Phenylenediamine, m-phenylenediamine, p-phenylenediamine, N, N, N ', N'-tetramethylethylenediamine, N, N, N', N'-tetramethyltrimethylenediamine, tetramethyl-p-phenylenediamine And so on. Of these, triethylamine, diphenylamine, triphenylamine and ethylenediamine are preferable. The above amine compounds may be added alone or in combination of two or more if necessary.

A suitable amount of the amine compound added to the non-aqueous electrolyte is 1 × 10 ^-3 to 1 × 10 ^-1 mol / liter.
When the addition amount is less than 1 × 10 ⁻³ mol / liter, the addition amount is too small to inactivate the negative electrode surface sufficiently, while the addition amount is 1 × 10 ⁻¹ mol / liter. When it exceeds liter, the charge / discharge reaction is hindered by the excessive increase of the inactive portion, and the effect of improving the cycle characteristics and the storage characteristics becomes small.

A feature of the present invention is that the decomposition of the non-aqueous electrolyte (solvent), which causes deterioration of charge / discharge cycle characteristics and storage characteristics, occurs on the surface of the negative electrode (carbon electrode) using a carbon material as a lithium ion storage material. The point is that a specific amine compound was added as an additive to the non-aqueous electrolyte in order to suppress the occurrence of charging. Therefore, for the other members constituting the battery such as the positive electrode material and the non-aqueous electrolyte solution, various materials conventionally proposed or put into practical use for lithium secondary batteries can be used without particular limitation.

For example, as the non-aqueous electrolyte, a single solvent or a mixture of ethylene carbonate, vinylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, 1,2-diethoxyethane, ethoxymethoxyethane, etc. LiPF ₆ , LiClO ₄ , LiBF ₄ ,
A solution in which a solute such as LiCF ₃ SO ₃ is dissolved in 0.7 to 1.5 mol / liter is exemplified.

Further, as the positive electrode material, LiNiO ₂ ,
Examples are lithium-transition metal composite oxides such as LiCoO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ .

[0015]

[Function] The amine compound inactivates the carbon electrode surface. Therefore, decomposition (reductive decomposition) of the non-aqueous electrolyte solution on the surface of the carbon electrode during charging is suppressed, and charge / discharge cycle characteristics and storage characteristics are improved.

[0016]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to the following examples, and various modifications may be made without departing from the scope of the invention. Is possible.

(Examples 1 to 19) [Positive electrode] LiOH and Ni (OH) ₂ Co (OH) ₂ were mixed in a mortar at a molar ratio of 2: 1: 1 and dried at 750 ° C in a dry air atmosphere. Heat treatment for 20 hours, crushed in an Ishikawa Raikai mortar, LiNi _0.5 Co with an average particle size of 5 μm
_0.5 O ₂ was obtained.

Then, LiNi as the positive electrode active material is used.
_0.5 Co _0.5 O ₂ , acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in a weight ratio of 90: 6: 4 to prepare a positive electrode mixture. After press-molding into a disk shape having a diameter of 20 mm with a molding pressure of ton / cm ² , heat treatment was carried out at 250 ° C. for 2 hours to produce a positive electrode.

[Negative Electrode] 95 parts by weight of graphite powder (carbon material) as a lithium ion storage material and 5 parts by weight of a 5% by weight N-methylpyrrolidone solution of polyvinylidene fluoride as a binder were kneaded to form a slurry. Prepared and applied this slurry to the surface of a copper foil as a negative electrode current collector, and 150 ° C
It was vacuum dried for 2 hours, rolled, and punched into a disk shape having a diameter of 20 mm to prepare a negative electrode.

[Non-Aqueous Electrolyte Solution] A non-aqueous electrolyte solution was prepared by dissolving 1 M (mol / liter) of lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1: 1. Then, the amine compound shown in Table 1 was added to this non-aqueous electrolyte at 1 × 10 ^-2 mol / liter.

[0021]

[Table 1]

[Battery Assembly] Flat-type batteries BA1 to BA19 of the present invention were assembled using the above positive electrode, negative electrode and non-aqueous electrolyte (battery size: diameter 24.0 mm, thickness 3.0).
mm). As the separator, a polypropylene microporous film was used, which was impregnated with the above non-aqueous electrolyte solution.

FIG. 1 is a cross-sectional view schematically showing the manufactured battery of the present invention. The battery A of the present invention shown in the drawing is a positive electrode 1, a negative electrode 2, a separator 3 for separating these electrodes 1 and 2 from each other, and a positive electrode. Can 4, negative electrode can 5, positive electrode current collector 6, negative electrode current collector 7
And an insulating packing 8 made of polypropylene.

The positive electrode 1 and the negative electrode 2 are housed in a battery case formed by positive and negative electrode cans 4 and 5 facing each other with a separator 3 impregnated with a non-aqueous electrolytic solution interposed therebetween. The positive electrode 1 is a positive electrode current collector. The negative electrode 2 is connected to the positive electrode can 4 via 6 and the negative electrode 2 is connected to the negative electrode can 5 via the negative electrode current collector 7, and the chemical energy generated inside the battery is converted into electrical energy from both terminals of the positive electrode can 4 and the negative electrode can 5. It can be taken out.

(Comparative Example) The same procedure as in Examples 1 to 19 except that the amine compound was not added to the non-aqueous electrolyte.
The comparative battery BC1 was assembled.

[Charge / Discharge Cycle Characteristics] Battery BA1 of the present invention
~ BA19 and comparative battery BC1 current density 1m
After charging to 4.3 V at A / cm ² , current density 3 mA
A charging / discharging cycle test was conducted with one cycle including a step of discharging up to 2.5 V at 1 / cm ² to investigate charging / discharging cycle characteristics. The discharge capacity at the first cycle and the discharge capacity at the 400th cycle of each battery are shown in Table 1 above.

As shown in Table 1, the batteries BA1 to BA19 of the present invention in which a specific amine compound was added to the non-aqueous electrolyte were:
Comparative battery B in which no amine compound was added to the non-aqueous electrolyte
400 compared to the discharge capacity at the first cycle compared to C1
The decrease in discharge capacity at the cycle is much smaller. From this, it is understood that the charge / discharge cycle characteristics are remarkably improved by adding the specific amine compound regulated in the present invention to the non-aqueous electrolyte. Further, the batteries of the present invention BA1 to BA
40 out of 19 BA1, BA9, BA10, BA12
The discharge capacity at the 0th cycle is particularly large. From this,
It is understood that triethylamine, diphenylamine, triphenylamine and ethylenediamine are particularly preferable as the amine compound.

[Relationship between Addition Amount of Amine Compound and Charging / Discharging Cycle Characteristics] The addition amount of triethylamine to the non-aqueous electrolyte is 8 × 10 ⁻⁴ mol / liter, 1 × 10 ⁻³ mol / liter, 5 × 10 ^-3 mol / liter, 5 × 10 ⁻² mol / liter, 1 × 10 ⁻¹ mol / liter, or 2 × 10 ⁻¹ mol / liter, Example 1 (Battery B of the present invention)
Inventive batteries BA20 to BA25 were assembled in the same manner as in A1).

Next, a charge / discharge cycle test was performed on these batteries under the same conditions as above, and the discharge capacity at the first cycle and the discharge capacity at the 400th cycle of each battery were examined.
Table 2 shows the results.

[0030]

[Table 2]

As shown in Table 2, the batteries BA21 to B of the present invention
Since the discharge capacity of the A24 at the 400th cycle is particularly large, the amount of triethylamine added to the non-aqueous electrolyte is 1 ×.
It can be seen that the range of 10 ⁻³ to 1 × 10 ⁻¹ mol / liter is preferable. It was confirmed that the same range was preferable for other amine compounds.

In the above embodiments, the case of applying the present invention to a flat type lithium secondary battery has been described as an example, but the shape of the battery of the present invention is not particularly limited.

[0033]

INDUSTRIAL APPLICABILITY The battery of the present invention is excellent in charge / discharge cycle characteristics and storage characteristics because the non-aqueous electrolyte is not easily decomposed on the surface of the negative electrode during charging.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a flat type lithium secondary battery assembled in an example.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator (impregnated with non-aqueous electrolyte)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Nishio 2-5-5 Keihan Hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-chome, Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A lithium secondary battery comprising a positive electrode, a negative electrode using a carbon material as a lithium ion storage material, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains an amine represented by the following chemical formula 1 and the following chemical formula: A lithium secondary battery comprising at least one amine compound selected from the diamines represented by 2. Embedded image [In formula, R < ¹ > -R < ³ > is mutually same or different and is a hydrogen atom, a C1-C4 alkyl group, or a phenyl group. ] [Chemical 2] [In the formula, X is an alkylene group having 1 to 4 carbon atoms or a phenylene group, and R ^{4 to} R ⁷ are the same or different from each other and are a hydrogen atom, a methyl group or a phenyl group. ] 2. A lithium secondary battery comprising a positive electrode, a negative electrode using a carbon material as a lithium ion storage material, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises triethylamine, diphenylamine, triphenylamine and ethylenediamine. A lithium secondary battery, to which at least one amine compound selected from the group is added. 3. The non-aqueous electrolyte contains 1 × of the amine compound.
The lithium secondary battery according to claim 1, which is added at a concentration of 10 ⁻³ to 1 × 10 ⁻¹ mol / liter.